1. Field:
This invention relates to bearings, and more particularly relates to bearing balls or rolls having controlled microstructures.
2. Prior Art:
Existing bearings are deficient, being non-uniform and non-symmetrical in chemical composition, microstructure, and physical and chemical properties. As a result, they wear or deform non-uniformly and uncontrollably, even from the very beginning of their services. In addition, they depend on external lubricants whose supply is also non-uniform and unpredictable.
Take, for example, the existing bearing ball. It is generally made by cutting from a long drawn or rolled rod a short piece that is roughly formed into a sphere by die-forging. The rough sphere is then ground into a sphere according to specific tolerances and heat-treated to achieve the required surface hardness. But the rod initially has a fibrous microstructure and is, therefore, anisotropic in its physical and chemical properties. Specifically, the rod is physically stronger and hence deforms less under load in the longitudinal direction (i.e., along the fibrous grains). On the other hand, chemical and corrosive agents tend to attack the ends of the rod and to penetrate preferentially along the fibrous grain boundaries; i.e., longitudinal attack is more rapid.
The fibrous nature of the original rod is distorted by the forming operation, which, in addition, introduces a distinct weakness in a meridian plane of the sphere. Heat treatment cannot homogenize the microstructure; in fact, nothing short of a melting and resolidification can remove the fibrous structure.
Rolled, drawn, or improperly grown materials have preferred orientations. The anisotropy in these materials causes wide variations in the physical properties, such as Young's modulus. In alpha-iron, for example, the observed maximum Young's modulus is 41.2.times.10.sup.6 psi, while the minimum is only 19.2.times.10.sup.6 psi, compared to 30.0.times.10.sup.6 psi for the average polycrystalline material. Under a loading stress of 200,000 psi, for example, a half-inch steel ball deforms elastically as little as about 2.4 mils but as much as 5.2 mils, a difference of 2.8 mils. The inner and outer races of a ball bearing consisting of ten half-inch steel balls and operating at 2,000 rpm are therefore each subjected to cyclic loadings at 333 cycles per second, with a maximum strain amplitude of 2.8 mils. Thus, the inner race, being under greater Hertzian stresses than the outer, often fails prematurely from fatigue. Hence, improving the mechanical and chemical isotropy of the bearing balls should be very effective in achieving bearing reliability. On the other hand, improving the initial dimensional sphericity (e.g., from 50 to 20 microinches at great cost) of an anisotropic half-inch ball elastically deformed up to 5.2 mils is relatively ineffective. In actual practice, even larger plastic deformations are also possible.
Other ball making methods, such as welding two hemispheres, give different but also anisotropic spheres. It is easy to see that an anisotropic sphere corrodes and distorts unevenly so that even a perfect sphere becomes, shortly after being put into service, a nonsphere.
In the case of cylindrical bearing made from a rod, the fibers are oriented parallel to the cylindrical axis, making the bearing weak to withstand load and to distort significantly and often non-uniformly, even on the first service.
Accordingly, an object of the invention is to provide improved ball or roller bearings;
A further object of this invention is to provide bearings which distort, wear, and corrode uniformly;
A broad object of the invention is to provide bearings which have reliable and long lives, even at high temperatures;
Another broad object of the invention is to provide ball or roller bearings having, respectively, center or axial symmetrical microstructures;
Another object of the invention is to provide bearings having self-lubricating properties with self-replenishing lubricants;
A still further object of the invention is to provide bearings with built-in lubricants at the grain boundaries to supply the bearing surface at precisely when, where, and to the amount needed.
Yet another object of the invention is to provide bearings with unique surface layers to better withstand fatigue and stresses or strains.